Refining of white metals



25 Per cent NazCOa 42.5

NaCl 1'! KCl 25.5 NaOH 15 Patented Mar. 14, 193a anasss PATENT OFFICE REFINING OF WHITE METALS Gustave E. Bohr, New York, N. Y., assignor to National Lead Company, New York, N. Y., a corporation of New Jersey No Drawing.

Application January 4, 1938,

Serial No. 183,319

8 Claims.

This invention relates to the elimination of impurity such as aluminum from metal and alloys, being usually present in only fractionalpercentages as, for example, in lead or lead tin alloys, such as solder or so-called white metals. Even as little as.00025 per cent aluminum in solder is definitely objectionable.

Heretofore the aluminum has been cleared by stirring sal ammoniac or sulphur into the metal, but the use of these clearing agents and all others of which Iam aware, produces ill-smelling smoke and fume, which is not only unpleasant to the workmen but pollutes the atmosphere in the locality where the operation is carried on and is particularly objectionable on that account.

The object is to provide means for clearing the metal of the contaminating aluminum with all the efiiciency and convenience of the present practice, but without producing the objectionable fume and smoke.

To this end, the invention consists, in its preferred form, of a compound containing thefol lowing ingredients in substantially. the proportions indicated:

uncovered, will give the signs of aluminum- The stirrer is then stopped andfree metal..

the melted salt mixture skimmed off. The ad'- dition of a pinch of sulfur will then 'finish the metal so that it will pour a perfect solder bar. If the solder is poured immediately after' skimming, the bars will have a logged appearance. To clear this, sal-ammoniac or rosin in very small amounts can be used but the amount of either sulfur, sal-ammoniac or rosin used for this is insignificant from the fume-producing. "point of view. The last detectable trace of aluminum' can be thus eliminated from the metal without producing objectionable fumes, Elaborate ventilation equipment is no longer needed and there is no pollution of the atmosphere. While the invention has been devised more particularly for removing aluminum, it is found also useful for removing zinc which responds similarly to aluminum.

The new compound has the property of eliminating the impurity Without affecting or removing any appreciable amount of tin. It is highly selective in its action notwithstanding that the case, some 200,000 times the amount of aluminum. It can be used a number of times before becoming exhausted and longer if replenished from time to time to make up for losses and the gradual thickening that is due to the impurity taken up. When the mixture has thickened as much as consistent with good operation, a separation of thick and thin salts can be made in a simple manner. The used salts are remelted in a kettle. Three layers will result. The top layer is thin-melting salts and is ladled off for further use.v The middle Player consists of thickened used-upsalts and this is ladled out metal carbonates, as I have discovered, is efiec- M tive by itself for clearing out small traces of aluminum, doing it selectively without afiecting the tin and the invention includes such use, al-

amount of tin present maybe, in an ordinary though sodium carbonate is best employed in con junction with the other components in the fortherefore the temperature of the treatment, 'so that the kettle, usually iron,'does 'not need'to be so highly heated and so that the loss by drossing, always greater with high temperatures, is

reduced. Various substances or combinations of substances may be used for this purpose, provided they are inert to the kettle contents, except the aluminum, and provided also they arenonfumefproducing. v

For example, a mixture of sodium or other alkali-metal .carbonate 50%, sodium chloride 20%; and potassium chloride30%, makes a comof salts producing a lower eutectic temperature will be found suitable.

Alkali hydroxides, although fumeless, would not ordinarily be selected when tin is present, because they are known to have a rapid action on that metal in metallic alloys, but I have found that within limits the presence of such hydroxides not only contributes to a lower melting point of the compound, but also accelerates its action and without any, noticeable effect on the tin. This may be the result either of a critical degree of dilution of the caustic by the other components as diluents, or of a certain inhibiting effect exercised by sodium carbonate. in any event, I have found that this effect occurs in the compound containing up to 15% of sodium hydroxide and this substance is accordingly used in the preferred formula above given. The use of more than this proportion is possible, but at the risk of tin loss.

It will be recognized that the proportions above given as preferred are approximately representative of a quaternary eutectic. Deviations therefrom are permissible, but only so long as the melting point of the compound, is kept within the practical limlt of 650 C.

I claim:

1. The process of removing aluminum impurity from tinny metals which consists in selectively removing the aluminum, with reference,

- to the tin, by treating the molten, tinny metal with'a molten alkali" metal carbonate.

2. The process of removing aluminum impurity from tinny metals which comprises selectively removing the aluminum, with reference to arouses the tin, by treating the molten tinny metal with a molten mixture of alkali metal carbonate and a non-fuming melting-point depressant.

3. The process of removing aluminum impurityv from lead-tin alloys which comprises selectively removing the aluminum, with reference to the tin, by treating the molten alloy metal with a molten mixture of an alkali carbonate and alkali-metal chloride in substantially eutectic proportions. v

4. The process of removing'aluminum impurity from lead-tin alloys which comprisesselectively removing the aluminum, with reference to the tin, by treating the molten metal with a mixture of an alkali metal carbonate and an alkali metal hydroxide.

5. The process of claim 4 in which the hydroxide is present in amount not exceeding about 15% of the mixture.

6. The process of claim 4 in which the hydroxide is present in amount not exceeding about 15% and the mixture contains also alkali metal chloride or chlorides.

7. As a clearing agent for contamination in lead-tin alloys, a mixture compound of alkali metal carbonate, hydroxide and halide in proportions melting below 650 C., the carbonate predominating. Y

8. As a clearing agent for aluminum contamination in tinny metals, a mixture compound of about 42.5% sodium carbonate, 17% sodium chloride, 25.5% potassium chloride and 15% sodium hydroxide.

GUSTAVE E. BEHR. 

